Apparently distinct from Rhodites radicum Riley

Rhodites radicum Gillette

Cynipidae

Diastrophus

Rubus flagellaris

Alabama

Arkansas

California

Connecticut

Delaware

Florida

Georgia

Illinois

Indiana

Iowa

Kansas

Kentucky

Louisiana

Maine

Maryland

Massachusetts

Michigan

Minnesota

Mississippi

Missouri

Nebraska

New Hampshire

New Jersey

New York

North Carolina

Ohio

Oklahoma

Pennsylvania

Rhode Island

South Carolina

Tennessee

Texas

Vermont

Virginia

West Virginia

Wisconsin

Nova Scotia

Ontario

Prince Edward Island

Quebec

Rubus occidentalis

Alaska

Arizona

Colorado

Idaho

Montana

Nevada

New Mexico

North Dakota

Oregon

South Dakota

Utah

Washington

Cynipid galls of the eastern United States

The North American Species of Diastrophus and their Galls

Diastrophus radicum

Diastrophus radicum, N. Sp.

Galls. On the roots of Rubus villosus [flagellaris], of very irregular shape, and varying in size from those of the shape and size of a pea to those two inches or more in length, and nearly an inch in diameter, and containing few or many larvae according to size. The galls are occasionally found on the part of the stalks of the blackberry which is below the surface. 

Galls found on plants of the genus Rubus

Diastrophus radicum Bassett

Diastrophus radicum BASSETT
Rhodites radicum GILLETTE

Gall. (Plate XXVII, Figs. 4, 5). On the roots of running blackberry or dewberry (Rubus canadensis), and probably allied species. Polythalamous. Brown, pithy and irregular in shape, varying in size from the shape of a pea of two inches or more in length and nearly an inch in diameter. Sometimes the entire root stalk above and below the surface of the ground, is surrounded by almost a solid mass of galls, measuring about three inches in diameter. 

Habitat: Canada to North Carolina; Michigan, Colorado. 

The fly is allied to D. turgidus, but may be readily separated by the absence of the brown color of the radial vein before reaching the second cross-vein. I have taken galls on the roots of the black raspberry or blackcaps (Rubus occidentalis) which may prove to be the same as D. radicum. According to Bassett the galls also may be found on the roots of the high bush blackberry (Rubus villosus). The types are in the American Museum of Natural History and American Entomological Society. 

Diastrophus radicum

raspberry
An irregular "root" gall on black raspberry

[Photo caption]
330. On wild raspberry. Adults May 2-21.

Diastrophus radicum Bassett, 1870 

Feeds on: Induces galls on Rubus corchorifolius L. f. (=villosus) and R. occidentalis L.

Distribution: United States: Colorado, Michigan, North Carolina

Catalog of Rose Gall, Herb Gall, and Inquiline Gall Wasps (Hymenoptera:Cynipidae) of the United States,Canada, and Mexico

Diastrophus radicum
Irregular bramble root gall wasp 

Host: Northern dewberry (Rubus flagellaris) and black raspberry (R. occidentalis). 

Gall location: On the roots, always below the surface of the soil. 

Description: A many-chambered swelling. Highly variable in shape and size, ranging from pea-shaped and less than a half centimeter to amorphous and globular, three centimeters in diameter. 

Range: Fairly widespread, from New England south to North Carolina. Some less-verifiable records indicate that this gall occurs as far south and west as Louisiana. 

The two host species on which this gall is found belong to two different subgenera, making the irregular bramble root gall rather unique amongst bramble galls. It is possible that galls on either host are actually separate species, but this has yet to be substantiated.

Field Guide to the Herb and Bramble Gall Wasps of North America